Methods and circuits for implementing programmable gamma correction

Abstract

A method of gamma correction includes selecting lower and upper reference curves corresponding to selected reference gamma values. A gamma correction curve is generated from a corresponding gamma correction value and cross-correlated with the upper and lower reference curves to generate a corresponding set of cross-correlation factors. The set of cross-correlation factors are stored and indexed to the corresponding gamma value. An input value is received for gamma correction with the corresponding gamma value. Data from the upper and lower reference curves indexed by the input value are then operated one with the cross-correlation factors to generate a gamma corrected output value.

Description

FIELD OF INVENTION [0001]The present invention relates in general to video processing and in particular to methods and circuits for implementing programmable gamma correction.BACKGROUND [0002]Gamma correction is a well-known technique for controlling the luminance (brightness) of the display pixels produced by cathode ray tube (CRT) displays and the like. Generally, the actual luminance of each pixel on the display screen has a non-linear relationship with the corresponding pixel data, such as the digital pixel data output from the DVD decoder. For most CRT displays, this non-linear relationship is the power function xγ, in which x is the brightness of the given pixel defined by the pixel data, γ is the gamma value for the given display system, and xγ is the actual brightness of the pixel produced by the display system. Normally, the values of x correspond to analog display control voltages between (0) and one (1) volt, and therefore for a given value of x, the brightness of the cor...

AI Technical Summary

Benefits of technology

[0010]Embodiments of the principles of the present advantages afford substantial advantages over the prior art. The use of reference curves and cross-correlation factors allow a range of gamma values to be programmed with minimal memory space. Specifically, the only memory spaces required are those necessary for storing the reference curves and the cross-correlation factors; memory space is not required for storing a large set of complete gamma correction curves since a range of gamma correction values are implicit in the stored set of cross-correlation values. Further, the desired gamma value for a given application can be directly selected, simply by writing to a single register. Additionally, the minimum error between the actual output values generated in accordance with the inventive principles and the corresponding ideal output values is reduced in view of conventional gamma correction schemes. In particular, the correlation-based (i.e. non-linear-based) interpolation of the present invention provides a substantially lower minimum error versus an ideal gamma correction curve than does conventional linear interpolation.

Problems solved by technology

The LUT approach, however, consumes a significant amount of memory space.

However, this second approach is still not memory efficient or easily programmable.

This approach introduces significant error, especially for lower luminescence values and also requires the re-programming of registers with pre-computed values to update the gamma correction curve.

This technique has improved error characteristics but still requires a significant amount of programming, after pre-computing the segment information, to change the gamma value.

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